Rockets and other space vehicles need a dry gas purge system to keep flammable vapors and water out of closed compartments while the rocket or vehicle goes through assembly, sits on the pad ready to launch, and is loaded with propellants, and during the actual flight. The vent system must prevent animal entry, gas back flow, explosive gas accumulation, and rain or moisture entry in order to protect sensitive equipment and instruments from damage or explosion.
Purge openings are also used to vent gases to prevent the internal pressure of a rocket and other space vehicles from reaching critical levels and damaging the rocket housing or internal components. High pressures may also cause rupture or explosions, putting observers, crews and other personnel at risk for injury.
It is also important to maintain purge gas circulation in general in rockets. Purge gases, such as dry nitrogen or helium, are circulated to keep components dry before propellants are introduced. As propellants are introduced, circulation must be increased to prevent the buildup of explosive gases or to prevent the creation of flammable liquefied air.
Purge openings are usually covered by a valve to prevent water and debris from entering the rocket cavities. The most common valve known in the art is a spring-loaded flapper valve. Pressure inside a rocket or other space vehicle pushes against the flapper door, causing the flap to open and gases to escape. The greater the internal pressure, the further the flap will open, and the greater the flow rate. With lower internal pressures, the flap will not open as far, and the flow rate will decrease.
One problem with flapper valves, however, is the inability to control the flow rate over a range of internal pressures. With flapper valves, in order to change the flow rate at a given internal pressure, the size of the purge valve itself must be changed or the springs replaced to allow more or less gas to pass through at a given pressure.
Other valve designs used in the past have attempted to overcome the problems known with flapper valves. However, these designs have incorporated multiple moving parts and are complicated, mechanical assemblies. Because of the number of moving parts, these valves are prone to damage, it is may be difficult or costly to continuously replace broken or disabled valves. Additionally, under certain high wind conditions, many of these devices can allow entry of humid, contaminated air to vented spaces.
Valve designs known in the art also generate significant noise as gases are purged. Because of the design of these valves, acoustical energy is propagated equally in all directions. At typical flow rates, workers, observers, and anyone near the rocket must wear ear protection to avoid injury.
Reed valves, a type of check valve known in the art, begin to overcome some of the problems known with flapper valves and complex mechanical valves. Reed valves use a pedal or pedals to selectively cover an aperture. When the pressure inside the valve is greater than the pressure outside the valve, the pedals are pushed away from the valve, allowing gases or fluids to pass through the valve opening.
Reed valves are most commonly used in two-stroke engines to control the fuel-air mixture admitted to the cylinder. Reed valves are specifically designed to open and quickly snap closed 100s of times a second in time with the engine's cycle. Current reed valves are not designed to open and remain open for long durations. Current reed valves are also not designed to maintain a cavity's pre-determined internal pressure and self-regulate flow rate to maintain the internal pressure or flow balance between cavities.
It is desirable to design a valve system which maintains a constant internal pressure and automatically adjusts to a desired flow rate.
It is desirable to design a valve system which limits the area in which harmful acoustical energy is released.
It is further desirable to design a valve system using modified off-the-shelf components with a minimal requirement for mechanical changes.